1. Field of the Invention
The present invention relates to a transfer scheme for speech and voice band signals and ISDN (Integrated Services Digital Network) digital signals which transfers speech and voice band signals and ISDN digital signals entered from an STM (Synchronous Transfer Mode) network to an ATM (Asynchronous Transfer Mode) network by assembling ATM cells from them and transferring ATM cells entered from the ATM network to the STM network by converting them into STM signals, at a connection point between the ATM network and the STM network.
2. Description of the Background Art
In the conventional STM network, signals are constantly transmitted through transmission channels regardless of presence or absence of communications such that unnecessary signals will occupy the transmission channels, and therefore it is impossible to realize an efficient utilization of transmission bandwidth. Also, at a time of transferring valid signals, the speech and voice band signals constantly occupy a certain transmission bandwidth even with respect to those signals which do not necessarily require the transmission bandwidth of one channel, so that it has been impossible to realize an efficient utilization of transmission channels.
Moreover, in the STM network in which signal compression is to be used, a compression scheme to be used is fixed, or the multiplexing of a plurality of signals after the compression is carried out in units of an input channel group that are fixed in advance. In a DCME (Digital Circuit Multiplication Equipment) used as a speech compression equipment, it is impossible to judge a type of each received signal when compressed signals are received, so that there is a need to constantly carry out inter-equipment communications between transmitting and receiving DCMEs in order to make a mutual synchronization.
As described, conventionally, signals after the compression can be multiplexed only in units of an channel group that are fixed in advance, the transmitting network is always the same network, and the network quality for signals is always the same regardless of signal types so that it has been impossible to carry out separate communications depending on a signal type and it has been impossible to transfer signals of each signal type to a network suitable for its required quality.
Also, in the case of changing the compression scheme dynamically with respect to one communication call at the transmitting side using a plurality of compression schemes, there is a need to constantly carry out communications for control purpose between the transmitting side equipment and the receiving side equipment and make a synchronization between these equipments in order for the receiving side to recognize the compression scheme applied to each received signal, and it is necessary to provide a transmission bandwidth for this purpose.